Evolution of the semiconductor manufacturing industry is placing greater demands on yield management and, in particular, on metrology and inspection systems. Critical dimensions continue to shrink, yet the industry needs to decrease time for achieving high-yield, high-value production. Minimizing the total time from detecting a yield problem to fixing it determines the return-on-investment for a semiconductor manufacturer.
Fabricating semiconductor devices, such as logic and memory devices, typically includes processing a semiconductor wafer using a large number of fabrication processes to form various features and multiple levels of the semiconductor devices. For example, lithography is a semiconductor fabrication process that involves transferring a pattern from a reticle to a photoresist arranged on a semiconductor wafer. Additional examples of semiconductor fabrication processes include, but are not limited to, chemical-mechanical polishing (CMP), etch, deposition, and ion implantation. Multiple semiconductor devices may be fabricated in an arrangement on a single semiconductor wafer and then separated into individual semiconductor devices.
Inspection processes are used at various steps during semiconductor manufacturing to detect defects on wafers to promote higher yield in the manufacturing process and, thus, higher profits. Inspection has always been an important part of fabricating semiconductor devices such as integrated circuits (ICs). However, as the dimensions of semiconductor devices decrease, inspection becomes even more important to the successful manufacture of acceptable semiconductor devices because smaller defects can cause the devices to fail. For instance, as the dimensions of semiconductor devices decrease, detection of defects of decreasing size has become necessary since even relatively small defects may cause unwanted aberrations in the semiconductor devices.
Electron beams are commonly used for inspection and other purposes during semiconductor manufacturing. Emittance of an electron beam is commonly measured, especially for accelerator and lithography applications. The electron beam emittance can be used to determine how bright the electron beam is. Most emittance implementations image the spot at various distances from an electron beam source. For example, the spot may be imaged a distance from the electron beam source ranging from a few millimeters to more than 1 cm. Some of these implementations slice the electron beam and image it at a distance through a slit or a pepper pot. Others of these implementations infer emittance based on the focused image of the electron beam.
These previous emittance measurement techniques are based on imaging the spot size at a distance. This can include imaging the electron beam between long distances, which can cause problems or require complicated electron beam optics. Aberration and resolution difficulties are generally encountered using these long distances.
Therefore, improved systems and methods to generate and measure electron beams are needed.